It's probably about the best you're going to get for your budget (although I must say that I've been away from music for quite a while so I'm not by any means up-to-date).
A quick run-through of what you can get and what it's good for...
* 'Proper' electric piano (or digital piano). This will have weighted keys and be velocity-sensitive. Won't have many voices or features. Speakers built in, but also outputs for external amplification and speakers, or headphones. As you pay more, it'll feel and sound more like a real piano.
* Keyboard (or synthesizer). This will usually be smaller (fewer keys, and sometimes the actual keys are smaller). It will have loads of voices and rhythms and features. Built-in speakers. As you pay more it will feel more piano-like, but not as good as the digital piano. Lower-end ones start off really cheap.
* MIDI controllers. These can be piano or keyboard style, but aren't a full package. They're just a keyboard-shaped controller, and you need another device to turn that into actual sounds. The weighted piano-style ones would start cheaper than a full digital piano.
Obviously there isn't a strict line between a digital piano and a keyboard, you might find something that's half way between the two.
From your budget I think you'll have to be looking at a keyboard, and I don't know of any problem with the one you've identified.
A keyboard is fine for a beginner. Your son will learn his way around the keyboard, where the notes are etc.
When he gets better and needs to really 'perform' a piece of music and not just play through it, then a keyboard won't help much with learning to do that.
The extra features and voices of a keyboard could work for or against you. It could make playing more fun, so he wants to practice more. Or you might find that he spends all his practice time messing about with the voices or setting his rendition of 'Fur Elise' to a nice bossa nova beat.
We're reaching the end of my knowledge now - piano was never my first instrument. Hopefully somebody else will know more, especially about the current market.